The high mortality rate for patients with newly diagnosed colorectal cancer is based on the low percentage of early stage disease at the time of surgery in symptomatic patients. Improved survival may be possible by screening asymptomatic patients with fecal occult blood tests coupled with radiologic and endoscopic diagnostic techniques. Evaluation of this approach requires controlled trials for demonstration of benefit. Longtern followup for mortality data is critical to this evaluation. Our controlled trial has been ongoing for 8 years with entry of 21,789 patients in screened and control groups with approximately 48,000 proctosigmoidoscopies and 30,000 occult blood tests performed to date. Our data suggest that screening with occult blood testing is feasible, with high patient compliance (80%) in a well motivated population, low rate of positive slides (2%), low false-positivity for neoplasia, high predictive value for neoplasia (30%), and favorable staging of detected cancers in the screened groups. Proctosigmoidoscopy and occult blood testing appear to be complementary. Fewer advanced cancers were found on the first screen in the study group than in the control group; incidence rates were approximately equal; survival is significantly better in the study group; and mortality appears to be higher in the control group. Continuation of our program will focus on followup for survival and mortality data in the control and screened groups. An effective follow-up program is now fully operative. Another goal is to complete at least 3 screens in all study patients. We will also continue to evaluate: the occult blood slide technique; factors that influence compliance; additional detected cancers; sensitivity and specificity of diagnostic techniques; the significance of adenoma detection and removal; interval cancers and adenomas; yield of rescreening; and cancer incidence. The level of funding requested is to support the large effort necessary to completely track the 22,000 patients entered into the study for successful achievement of these longterm objectives.